Enhanced D-ribose biosynthesis in batch culture of a transketolase-deficient Bacillus subtilis strain by citrate.

In this study, the effects of citrate addition on D-ribose production were investigated in batch culture of a transketolase-deficient strain, Bacillus subtilis EC2, in shake flasks and bioreactors. Batch cultures in shake flasks and a 5-l reactor indicated that supplementation with 0.2-0.5 g l(-1) of citrate enhanced D: -ribose production. When B. subtilis EC2 was cultivated in a 15-l reactor in a complex medium, the D: -ribose concentration was 70.9 g l(-1) with a ribose yield of 0.497 mol mol(-1). When this strain was grown in the same medium supplemented with 0.3 g l(-1) of citrate, 83.4 g l(-1) of D-ribose were obtained, and the ribose yield was increased to 0.587 mol mol(-1). Addition of citrate reduced the activities of pyruvate kinase and phosphofructokinase, while it increased those of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Metabolic flux distribution in the stationary phase indicated that citrate addition resulted in increased fluxes in the pentose phosphate pathway and TCA cycle, and decreased fluxes in the glycolysis and acetate pathways.